Brush for dynamo-electric machinery



NOV. 5, 1929. w c KALB 1,734,811

BRUSH FOR DYNAMO ELECTRIC MACHINERY Filed May 19, 1925 W 6 M, mvsmoa BYm ATTORNEYS Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE WARREN C.KALB, OI BRADFORD, PENNSYLVANIA, ASSIGNOR, BY HESNE ASSIGN- MENTS, TONATIONAL CARBON COMPANY, INC., 01' NEW YORK, N. Y., A CORPORA- TION OFNEW YORK BRUSH FOR DYNAKO-ELECTRIC MACHINERY Application filed Kay 19;1925. Serial No. 81,410.

a My present invention relates to commutator brushes and processes formaking same. In certain types of electrical machines it is desirable toemploy brushes having a relatively high specific electrical resistancemeasured in the longitudinal direction. In accordance with the presentinvention I propose to obtain such relatively highlongitudinalresistance by using a bond which in its final state is relativelynon-conducting. At the same time it is desirable to maintain a highratio of transverse to longitudinal specific electrical resistance inorder to reduce as far as possible the leakage of current from onecommutator segment to an adjoining one through the brush or brushes withwhich they are in similtaneons contact To the attainment of theforegoing and related'ends, I preferably employ as the basis of myimproved product graphite in flake form, the particles of which may bebonded by means of an organic binder which, however, in the finalproduct is only partially car bonized whereby the electrical resistanceof the product is increased. By employing flake graphite I takeadvantage of the fact that when compressed the individual flakes 0rlaminae arrange themselves flatwise to the di rection of pressure,whereby the electrical resistance in the line of pressure is renderedgreater than in a direction at right angles thereto for the reason thata greater number of contacts are formed in the transverse direction.

I have illustrated one embodiment of my invention in the accompanyingdrawing in which Figure '1 is a perspective view of the plate from whichbrushes constructed in accordance with my invention are cut;

the brushes; and

Fig. 3 is aside view of the same.

. It should be remembered that for the sake of clearness the flakes orgrains of graphite and the binder are drawn to a greatly exaggeratedscale.

In carryin out my invention I may mix two and onealt pounds flakegraphite with four fluid ounces of black strap molasses diluted withfour ouncesof water, the mixing Fig. 2 is a diagrammatic top view of oneof being carried out at a temperature of 150 F. and continued until themoisture is nearly all driven off and lumps disappear leaving the entiremixture in the'form of a loose powder. Plates of desired size are nowmade at a pressure of thirty tons per square inch applied flatwisethereof as shown by the arrow P in Fig. 1, a hydraulic press of suitabletype being used for this purpose. The plates are then baked at atemperature of 420 F., the temperature rise being spread over aninterval of about twenty-four hours. The plates thus made are then cutinto brushes of the desired size and shape along lines a and b and otherlines parallel thereto.

In lieu of a partially carbonized bond, I may employ other bonding mediaof comparatively high electrical resistance. Thus I may use sodiumsilicate for this purpose either alone or in connection with an organicbinder such as tar or the like. The action of the sodium silicate is tocoat the particles of graphite or other base material with a thin filmwhereby the overall specific electrical resistance of the brush isincreased, while at the same timethe mechanical strength of the finalproduct is improved.

In cutting up the plates into brushes, the cutting is carried out sothat the flatwise dimension of the plates corresponds to that of thebrushes. When the flake material, such as flake graphite, is compacted,the particles tend to arrange themselves so that they are disposedflatwise to the line of pressure whereby the specific electricalresistance measured along the direction of the original pressure isgreater than that measured at right angles thereto. The reason for thisis that due to the flat shape of the particles there are more contactsin the line of pressure than in the direction at right angles to suchline. Hence in the finished brush, the specific electrical resistancemeasured transversely will be greater than that measured in the longi:tudinal direction. I

My improved product is characterized by comparatively high longitudinalelectrical resistance. i. e., between .0010 and .0020 ohms per inch cubeand a .high ratio of transverse to longitudinal specific electricalresistance, as for example 1 or higher.

It will be understood that the above specific example is given by way ofillustration and that I do not limit myself to the exact quantities andvalues given. Thus, other organic bonding agents than the ones mentionedmay be used, examples being sulphite liquor, sugar, etc.

What I claim is:

1. The process of making a commutator brush which comprises forming amixture of 10 parts of flake graphite, one part of molasses and one partof water, partially drying the mixture, forming the mixture into plates,compressing the plates in one direction by a. pressure of at least 25tons to the square inch, baking the plates and cutting the p ates intobrushes in such a direction that the direction of pressure will be alongthe thickness of the brush.

2. The process of making a commutator brush which comprises forming amixture of 10 parts of flake graphite, one part of molasses and one partof water, drying the mixture at a temperature of F. until most of themoisture is driven off, forming the mixture into plates, compressing theplates in one direction by a pressure in excess of 25 tons to the squareinch and baking the plates at a temperature of 420 F.

In testimony whereof I have afiixed my signature to this specification.

WVARREN C. KALB.

